Conventional double-sided processing of hard memory disks involves a number of discrete steps. Typically, twenty-five substrate disks are placed in a plastic cassette or carrier, axially aligned in a single row. Because the disk manufacturing processes are conducted at different locations using different equipment, the cassettes are moved from work station to work station. For most processes, the substrate disks are individually removed from the cassette by automated equipment, both sides or surfaces of each disk are subjected to the particular process, and the processed disk is returned to the cassette. Once each disk has been fully processed and returned to the cassette, the cassette is transferred to the next work station for further processing of the disks.
More particularly, in a conventional double-sided disk manufacturing process, the substrate disks are initially subjected to data zone texturing. Texturing prepares the surfaces of the substrate disks to receive layers of materials which will provide the active or memory storage capabilities on each disk surface. Texturing may typically be accomplished in two ways: fixed abrasive texturing or free abrasive texturing. Fixed abrasive texturing is analogous to sanding in which a fine grade sand paper or fabric is pressed against both sides of a spinning substrate disk to roughen or texturize both surfaces. Free abrasive texturing involves applying a rough woven fabric against the disk surfaces in the presence of a slurry. The slurry typically contains diamond particles, which perform the texturing, a coolant to reduce heat generated in the texturing process and deionized water as the base solution. Texturing is typically followed by washing to remove particulate generated during texturing. Washing is a multi-stage process and usually includes scrubbing of the disk surfaces. The textured substrate disks are then subjected to a drying process. Drying is typically performed on all of the disks from a cassette at the same time. Following drying, the textured substrate disks are subjected to laser zone texturing. Laser zone texturing does not involve physically contacting and applying pressure against the substrate disk surfaces like data zone texturing. Rather, a laser beam is focused on and interacts with discrete portions of the disk surface, primarily to create an array of bumps for the head and slider assembly to land on and take off from. Laser zone texturing typically is performed one disk at a time. The disks are then washed again. Following a drying step, the disks are individually subjected to a process which adds layers of material to both surfaces for purposes of creating data storage capabilities. This can be accomplished by sputtering, deposition or by other techniques known to persons of skill in the art. Following the addition of layers of material to each surface, a lubricant layer typically is applied. The lubrication process can be accomplished by subjecting an entire cassette of disks to a liquid lubricant; it does not need to be done one disk at a time. Drying is also performed on an entire cassette of disks at one time. Following lubrication, the disks are individually subjected to surface burnishing to remove asperities, enhance bonding of the lubricant to the disk surface and otherwise provide a generally uniform finish to the disk surface. Following burnishing, the substrate disks are also subjected to various types of testing. Examples of testing include glide testing to find and remove disks with asperities that could affect flying of the head/slider assembly and certification testing which is writing to and reading from the disk surfaces. Certification testing is also used to locate and remove disks with defects that make the surface unusable for data storage. The finished disks can then be subjected to a servo-writing process and placed in disk drives, or placed in disk drives and then subjected to servo-writing.
As part of the washing and drying process, organics dissolved in the water are left behind when the water evaporates, resulting in non-volatile residue or nodules deposited on the surface of the disk. These nodules, when analyzed, are found to contain carbon. These nodules may impact the grain formation of the magnetic layers creating discrete areas or zones on the disk surface where data is no longer capable of being written or read. The nodules also create surface irregularities that affect the interface between the disk surface and the read/write head of the disk drive. These irregularities may then cause failure during the glide testing, or later on as the lubricant in the area gets picked up by the read/write head, causing depletion of the lubricant and eventually head crash, i.e. total drive failure. Moreover, these can be a latent problems that worsens over time. This can cause significant problems for the owner of the disk drive containing one or more of these disks, potentially leading to lost data.
A typical disk drying process and related apparatus is shown in FIGS. 1A and 1B. A lifter arm assembly 10 holding two three-point lifter nests 12 is shown in FIG. 1A. As illustrated, a plurality of disks are initially engaged and positioned relative to the lifter arm assembly 10 by a horizontal transfer apparatus 14 that supports the aligned row of disks along the outer diameter (OD) of the disks. The engagement of the disks by the horizontal transfer apparatus 14 is also shown in FIGS. 2 and 3. The horizontal transfer apparatus generally comprises a pair of elongate arms 14a and 14b, with a row of serrations or notches for engaging the outer edge or perimeter of the disks 18. The arms 14a and 14b move toward and away from the disks 20 to engage and disengage the disks. The horizontal transfer apparatus 14 positions the plurality of disks 20 in alignment with the lifter cassettes 12. As illustrated in FIG. 1B, the lifter nests 12 each have three longitudinally oriented rows of teeth or notches 16 that engage each disk at three points on the outer diameter of the disks. The lifter arm assembly 10 raises to a position where the three rows of teeth 16 in the nests 12 engage the bottom perimeter edge of the disks 18. The horizontal transfer arms 14a and 14b separate such that the disks are supported solely by the nests 12 and the lifter arm assembly 10 lowers the nests 12 and disks 20 into a liquid bath (not shown). After a predetermined amount of time passes, the lifter arm assembly 10 raises the nests 12 above the bath and, in the presence of an inert gas flow, the disks are dried. As the liquid from the bath runs off the disks, the liquid collects at the three contact points where the outer edge of each disk is engaged or contacted by the support notches 16 in the nests 12. During the drying process the entire disk surface dries, except at the three points when the nests 12 contact the disks 18. After the disks are returned to the horizontal transfer apparatus 14, the moisture trapped by the three contact points dries and leaves a chemical residue on the disk surface. These residual or contact marks 18, formed on both surfaces 20a and 20b of a disk 20, are illustrated in FIGS. 4A and 4B. As noted above, the disks are subsequently subjected to process steps where layers of metal or metal alloys are deposited on the surfaces 20a and 20b of the disks over the contact areas 18. Over time and with exposure to air, the residual chemicals comprising the contact marks may cause corrosion or a growing defect area at these locations. The corrosion may occur in the data zone of the disk or spread to the data zone of a disk as the area of the defect spreads. This contamination leads to areas of the disk that are unusable for data storage and results in defective disks. Because the corrosion may occur slowly over time, a problem may arise long after the disks have been placed in a disk drive and used by the owner of the drive. As a result, data previously stored at these locations may be lost.